Cambodia's opposition leader Kem Sokha (left) sitting with his mother Sao Nget while confined by the government at his residence in Phnom Penh. Cambodia's strongman leader Hun Sen batted down speculation on September 19 that he caved to international pressure after an opposition leader was relased from jail, claiming the decision was made for (AFP/Chhea Bunnarith)

Cambodian prime minister Hun Sen batted down speculation Wednesday that he caved to international pressure after an opposition leader was released from jail, claiming the decision was made for his ailing foe's health and safety.

Kem Sokha, the co-founder of the now-defunct Cambodia National Rescue Party, was arrested on treason charges in September two months before the Supreme Court dissolved his party.

The moves came during a sweeping crackdown led by the 66-year-old strongman and paved the way for an easy election victory in July that was lambasted as a sham.

But in the aftermath of the vote Hun Sen has returned to a pattern of easing up on dissent and scores of activists and former opposition members have been freed.

Kem Sokha was the most prominent of those let go and his September 10 release on bail fuelled theories that Hun Sen was worried about the country's large clothing industry losing duty-free access to European markets.

European parliamentarians have floated the possibility of revisiting the trade scheme.

But the bombastic head of the ruling Cambodian People's Party, who has been in power for more than 33 years, told garment workers in a speech that he did not bow to "international pressure".

"It was just the change of the location of detention in case he dies in prison and causes trouble to the government," Hun Sen said, not mentioning the duty-free deal.

He added that the decision was prompted by "humanitarian and safety concerns for the suspect".

Sokha, 65, spent more than a year in a remote prison near the Vietnamese border before his release.

Over the course of his detention he was repeatedly denied bail even as his lawyers pointed to Sokha's high blood pressure and diabetes.

The conditions of his bail are severe. He is supposed to stay within a block radius of his residence and is forbidden to meet with foreigners or host political rallies.

Lawyer Meng Sopheary said the opposition leader was taking medication regularly but still needed a full examination.

"He will be happy if he has his full freedom," she told AFP.

The US has expanded travel sanctions against senior Cambodian officials in response to the election but so far the country has received little real blowback for the deeply flawed poll.

The ruling party says it won more than 80 percent of the vote and all seats in parliament, turning Cambodia into a one-party state.

But critics claim the election was marred by the absence of any credible contender and voter intimidation in the run-up to the poll.

Before its dissolution Sokha's party had posed the biggest threat to Hun Sen in recent memory, winning more than 43 percent of the vote in the 2013 vote.

Hun Sen has remained defiant in the face of criticism, telling a regional summit in Hanoi last week that western governments should stay out of Southeast Asian politics.